My group and I have been arguing this for a couple hours now. The stacking of IUD and uncanny. The level 10 ninja in our group wants to take a level in shadowdancer. He says because he already has IUD from his ninja he want be flanked by a level 14 or lower. I have argued he can't stack his uncanny dodge bonus from the shadow dancer because he has not achieved that ability from his shadowdancer yet. The rules seem a little vague to us so I was wondering if there was an errata or somethung

The Shadowdancer prestige class is poorly written and designed, this lag of one level in Improved Uncanny Dodge followed by a two-level bump is a good illustration of this poor design.

Part of the role of the game master is to do copy editing on poorly written rules. I'd rule that levels of Shadowdancer stack with those of rogue/ninja for the purpose of Improved Uncanny Dodge - and not as a favour to the player as rule of cool but as an arbiter in fairness.